1. Field of Invention
The present invention generally relates to a low power protection circuit, and more particularly to a low power protection circuit adapted for a voltage pump circuit of a dynamic random access memory (DRAM) with dual operating voltages.
2. Description of Prior Art
Along with the rapid development of science and technology at the present, semiconductor memories are widely used in currently electronic products. In a conventional dynamic access memory (DRAM), dual operating voltages are used in the DRAM. The second operating voltage with lower voltage level is used to allow the DRAM to function correctly. The first operating voltage with higher voltage level is used to help make a voltage pump circuit of the DRAM more efficient.
Referring to FIG. 1, FIG. 1 is a waveform plot of the conventional DRAM. During a timing period T0, the operating voltages VDD1 and VDD2 are raised, and the operating voltages VDD1 reaches to a first stable voltage level earlier. The pump output voltage VCCP generated by the voltage pump circuit may go to runaway (too high) when the operating voltages VDD1 reaches to the first stable voltage level and the second operating voltage VDD2 fails to reach a second stable voltage level. After a timing period T1 and during a timing period T2, the first and second operating voltages VDD1 and VDD2 go to low, and the second operating voltage VDD2 is reduced earlier. The pump output voltage VCCP generated by the voltage pump circuit may go to runaway again when the first operating voltage VDD1 is kept at the first stable voltage level, and the second operating voltage VDD2 is reduced too low.